Investigation of ultrasonic vibrations of wire-bonding capillaries

Ultrasonic energy is widely used in wire bonding for microelectronics packaging. It is necessary to ensure that the maximum ultrasonic vibration displacement occurs at or near the tip of the bonding tool (capillary) for optimal performance. In this study, amplitude profiles of ultrasonic vibrations along capillaries were measured with load using a laser interferometer. This provided valuable information in understanding and improving capillary performance. The method was applied to real time applications to optimize capillary designs and bonding processes for specific bonding applications. First, the application of a new capillary material with different zirconia compositions was evaluated. The new material with certain amount of zirconia composition showed that it was the capillary material of choice for ultra-fine pitch wire bonding. Next, comparative analysis was conducted to investigate the ultrasonic energy transfer of a new ‘slimline’ bottleneck and the conventional bottleneck. The actual bonding response of the molded slimline bottleneck showed comparable performance with the ground conventional bottleneck using the same bonding parameters. Finally, optimization of a 60-μm-bond-pad-pitch process was performed on a wire bonder. Within the optimized parameter ranges, the ultrasonic displacement of the capillary was monitored. For all possible combinations of bond force and bond power, the ultrasonic displacement of the capillary increased with increasing bond power, without drastic changes caused by bond force changes. This indicated that the selected process window was located in a stable region.